JP3550216B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and more particularly to an apparatus having an electrically heated catalyst.
[0002]
[Prior art]
Since a catalyst that purifies the exhaust gas of an internal combustion engine requires time to activate during cold start of the engine, an electrically heated catalyst that is electrically heated to accelerate the activation has been used. More known.
[0003]
As an energization control method for the electrically heated catalyst, an energization time is set in accordance with the detected engine temperature and the like, and power is supplied from the battery over the set energization time so that a desired catalyst temperature can be obtained. The above-mentioned method is conventionally known (Japanese Patent Laid-Open No. Hei 4-279718).
[0004]
[Problems to be solved by the invention]
In general, when the characteristics of a catalyst deteriorate due to aging, the temperature required to activate the catalyst tends to increase.Therefore, it is necessary to change the target temperature in accordance with the aging of the catalyst and perform energization control. is there.
[0005]
However, since the above-mentioned conventional control method controls only the energization time using a battery as a power source, there are the following problems when applied to recent control of a catalyst having a small heat capacity. That is, for a catalyst having a relatively large heat capacity, the catalyst temperature can be controlled to the target temperature by controlling only the energizing time. However, when the heat capacity becomes small, the catalyst temperature rises rapidly. However, when the catalyst is new, the temperature is too high, and the durability of the catalyst may be deteriorated, or the catalyst carrier may be mechanically broken. On the other hand, if it is attempted to eliminate such a problem in the state of a new product, there is a problem that the temperature rise is too slow at the time of characteristic deterioration, which causes deterioration of exhaust gas characteristics immediately after starting the engine.
[0006]
The present invention has been made in view of this point, and accurately controls the temperature of the catalyst in response to the time-dependent change of the electrically heated catalyst, so that excessive exhaust temperature in a new state and exhaust in the case of characteristic deterioration are caused. An object of the present invention is to provide an exhaust gas purifying device capable of preventing deterioration of gas characteristics.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides an alternator driven by an internal combustion engine to generate electric power, a regulator means for controlling a generated voltage of the alternator, and an exhaust system of the engine, the electric power being generated by the alternator. An electrically heated catalyst electrically heated by electric power, a time-varying state detecting means for detecting a time-varying state of the electric heating catalyst , and a power generation voltage determined according to an output of the time-varying state detecting means ; A regulator control means for controlling the regulator means so as to supply the determined power generation voltage from the alternator to the electrically heated catalyst is provided.
[0008]
Further, with the operating condition detecting means for detecting an operating condition of the engine, said regulator control means includes a Turkey to determine the generator voltage in accordance with the engine operating state of the detection is desirable.
[0009]
Further, the regulator control means further determines a time at which the generated voltage is to be supplied to the electrically heated catalyst according to the detected engine operating state , and the determined time is determined over the determined time. It is desirable to control the regulator means to supply the generated voltage from the alternator to the electrically heated catalyst .
[0010]
[Action]
According to the exhaust gas purifying device of the first aspect, electric power is supplied from the alternator to the electric heating type catalyst, and the power generation voltage of the alternator is controlled according to the detected time-dependent change state of the electric heating type catalyst .
[0011]
According to the exhaust gas purifying device of the second aspect, the power generation voltage of the alternator is controlled according to the detected engine operating state.
[0012]
According to the exhaust gas purifying device of the third aspect, the time for supplying electric power to the electrically heated catalyst is further controlled in accordance with the detected engine operating state.
[0013]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0014]
FIG. 1 is an overall configuration diagram of an internal combustion engine and a control device therefor according to one embodiment of the present invention. A throttle valve 3 is arranged in the intake pipe 2 of the engine 1. A throttle valve opening (θTH) sensor 4 is connected to the throttle valve 3, and outputs an electric signal corresponding to the opening of the throttle valve 3 to supply the electric signal to the ECU 5.
[0015]
The fuel injection valve 6 is provided for each cylinder between the engine 1 and the throttle valve 3 and slightly upstream of the intake valve (not shown) of the intake pipe 2, and each injection valve is connected to a fuel pump (not shown). At the same time, it is electrically connected to an electronic control unit (hereinafter referred to as “ECU”) 5, and the opening time of the fuel injection valve 6 is controlled by a signal from the ECU 5.
[0016]
On the other hand, immediately downstream of the throttle valve 3, an intake pipe absolute pressure (PBA) sensor 8 is provided via a pipe 7, and the absolute pressure signal converted into an electric signal by the absolute pressure sensor 8 is supplied to the ECU 5. Is done. Further, an intake air temperature (TA) sensor 9 is attached downstream thereof, detects the intake air temperature TA, outputs a corresponding electric signal, and supplies the electric signal to the ECU 5.
[0017]
The engine water temperature (TW) sensor 10 mounted on the main body of the engine 1 is composed of a thermistor or the like, detects the engine water temperature (cooling water temperature) TW, outputs a corresponding temperature signal, and supplies it to the ECU 5.
[0018]
An engine speed (NE) sensor 11 and a cylinder discrimination (CYL) sensor 12 are mounted around a camshaft or a crankshaft (not shown) of the engine 1. The engine speed sensor 11 outputs a TDC signal pulse at a crank angle position before a predetermined crank angle with respect to the top dead center (TDC) at the start of the intake stroke of each cylinder of the engine 1 (every 180 degrees of crank angle in a four-cylinder engine). The cylinder discrimination sensor 12 outputs a cylinder discrimination signal pulse at a predetermined crank angle position of a specific cylinder, and these signal pulses are supplied to the ECU 5.
[0019]
In the exhaust pipe 13 of the engine 1, an upstream oxygen concentration sensor (hereinafter, referred to as an "upstream O2 sensor") 20F, an electrically heated catalyst (hereinafter, referred to as "EHC") 16, a start catalyst 17, and a three-way catalyst are arranged in this order from the upstream side. 18 and a downstream oxygen concentration sensor (hereinafter referred to as “downstream O2 sensor”) 20R. The O2 sensors 20F and 20R detect the oxygen concentration in the exhaust gas, supply the detection signal to the ECU 5, and the catalysts 16, 17, and 18 purify components such as HC, CO, and NOx in the exhaust gas. Here, the start catalyst 17 is a small catalyst provided mainly for purifying exhaust gas immediately after the start of the engine.
[0020]
The exhaust pipe 13 is further connected to a passage 14 for supplying secondary air upstream of the EHC 16, and an air pump 15 is provided in the passage 14.
[0021]
The EHC 16 and the air pump 15 are connected to the ECU 5, and their operations are controlled by the ECU 5. Further, the three-way catalyst 18 is provided with a catalyst temperature sensor 19 for detecting the temperature TCAT, and a detection signal is supplied to the ECU 5.
[0022]
The alternator 21 driven by the engine 1 is connected to the ECU 5 via a regulator 22, and the generated voltage is controlled by the ECU 5.
[0023]
The ECU 5 shapes input signal waveforms from various sensors, corrects a voltage level to a predetermined level, and converts an analog signal value to a digital signal value. The input circuit 5a has a function of a central processing unit (hereinafter referred to as a “CPU”). 5b, a storage means 5c for storing various calculation programs executed by the CPU 5b and calculation results, and an output circuit 5d for outputting control signals for the fuel injection valve 6, the air pump 15, the EHC 16, the regulator 22, and the like. Is done.
[0024]
The CPU 5b calculates the valve opening time TOUT of the fuel injection valve 6 based on the above-mentioned various engine parameter signals by the following equation, and also performs the processing of calculating the energization time TON of the EHC 16 and the supply voltage VEHC as described later. It outputs a control signal according to the calculation result.
[0025]
TOUT = TI × KO2 × K1 + K2 (1)
Here, TI is a basic fuel amount, specifically, a basic fuel injection time determined according to the engine speed NE and the intake pipe absolute pressure PBA. A TI map for determining the TI value is stored in the storage means. 5c.
[0026]
KO2 is an air-fuel ratio correction coefficient calculated based on the outputs of the O2 sensors 16 and 17, and the air-fuel ratio (oxygen concentration) detected by the upstream O2 sensor 16 matches the target air-fuel ratio during the air-fuel ratio feedback control. During the open loop control, and is set to a predetermined value according to the engine operating state.
[0027]
K1 and K2 are other correction coefficients and correction variables calculated according to various engine parameter signals, respectively, and are values for optimizing various characteristics such as fuel consumption characteristics and engine acceleration characteristics according to the engine operating state. Is set to
[0028]
FIG. 2 is a circuit diagram showing a connection state of the ECU 5, the alternator 21, the regulator 22, the heater resistor 24 of the EHC 16, the motor 27 of the air pump 15, and the battery 29. Note that the EHC 16 of this embodiment is configured to function as a heater by energizing the catalyst itself, and the resistance is represented as a heater resistance 24.
[0029]
In the figure, the output side of the alternator 21 is connected to the terminal 23a of the changeover switch 23, and the terminal 23c of the changeover switch 23 is connected to one end of the heater resistor 24. The other end of the heater resistor 24 is grounded, and an EHC current sensor 25 for detecting a heater current IEHC is provided in the middle of the connection line 31.
[0030]
The terminal 23 b of the changeover switch 23 is connected to the positive electrode of the battery 29 and the terminal 26 a of the on / off switch 26, and the terminal 26 b is connected to one end of the motor 27. The other end of the motor 27 is grounded, and a pump current sensor 28 for detecting a pump current IAP is provided in the middle of the connection line 33.
[0031]
The negative electrode of the battery 29 is grounded, and the positive electrode is connected to the ECU 5.
[0032]
The switches 23 and 26 are connected to the ECU 5 and are configured to be switchable by a control signal from the ECU 5. Normally, the switch 23 is in a state where the terminals 23a and 23b are connected as shown in FIG. 2, and the switch 26 is turned off, and the switching is controlled as needed immediately after the engine is started. The connection lines 30 and 32 are connected to the EUC 5, and the ECU 5 detects the EHC voltage VEHC and the pump voltage VAP. Further, the current sensors 25 and 28 are also connected to the ECU 5, and their detection signals are supplied to the ECU 5. These current sensors 25 and 28 are provided for detecting abnormalities such as disconnection.
[0033]
FIG. 3 is a flowchart of a process for performing power supply control to the heater resistor 24.
[0034]
In step S1, it is determined whether or not the precondition is satisfied (whether or not the ignition switch is turned on), and if not, the process is immediately terminated. When the precondition is satisfied (when the ignition switch is turned on), the detected values of the engine water temperature TW and the intake air temperature TA are read (step S2). Next, the TON map and the VEHC map set according to the TW value and the TA value are searched, and the energizing time (EHC on time) TON of the heater resistor 24 and the supply voltage VEHC to the EHC 16 are determined (step S3).
[0035]
As shown in FIG. 4, the TON map is set such that the TON value decreases as the intake air temperature TA increases and as the engine coolant temperature TW increases. It is to be noted that TON is set to 0 since power is not supplied above the predetermined temperatures TAH and TWH. 5A and 5B, the VEHC map is set such that the VEHC value tends to decrease as the intake air temperature TA increases and as the engine coolant temperature TW increases. Therefore, the power supplied to the EHC 16 is controlled as shown in FIG. The VEHC value is set to, for example, about 30 V during a cold start. As a result, the supply current can be reduced to about 比 べ compared to the case where power is supplied from the battery.
[0036]
In the following step S4, a KDG table shown in FIG. 6A is searched according to a determination time TCHK which is a parameter indicating the degree of deterioration of the catalyst detected by a method described later, and a time-dependent change correction coefficient KDG is calculated. The determination time TCHK is a parameter that decreases as the catalyst deteriorates and the oxygen storage capacity decreases, and is set such that the KDG value increases as the TCHK value decreases.
[0037]
The time-dependent change correction coefficient KDG is calculated using a table set according to the traveling distance MLG of the vehicle on which the engine 1 is mounted, as shown in FIG. As shown, the calculation may be performed using a table set according to the number NON of energizations of the EHC 16. The KDG tables shown in FIGS. 7B and 7C are set so that the KDG value increases as the traveling distance MLG or the number of energizations NON increases. In this embodiment, the maximum value of the KDG value is set to 1.0.
[0038]
Next, the VEHC value is corrected by multiplying the EHC voltage VEHC determined in step S3 by the aging correction coefficient KDG (step S5). As a result, the VEHC value is set to the smallest value when the catalyst is new, and is set so as to increase as the catalyst deteriorates. Therefore, the temperature of the catalyst is accurately controlled in accordance with the aging of the EHC 16. In addition, it is possible to prevent the exhaust gas characteristics from being deteriorated when the temperature is excessively increased and the characteristics are deteriorated in a new state.
[0039]
In a succeeding step S6, it is determined whether or not the engine speed NE is equal to or higher than a predetermined engine speed NEK (for example, 400 rpm) for judging complete explosion. If NE <NEK, this process is immediately terminated, while NE ≧ NEK. If so, the changeover switch 23 is switched to the terminal 23c side, and the alternator output voltage VALT is controlled to be the VEHC value corrected in step S5 to supply power to the EHC 16 (step S7). Then, after the passage of the power-on time TON, the alternator output voltage VALT is reduced to the normal output voltage VCHG (for example, 14.5 V), and the switch 23 is switched to the terminal 23b (step S8).
[0040]
Note that the precondition in step S1 in FIG. 3 may be satisfied when the ignition switch is turned on and the engine coolant temperature Tw and / or the catalyst temperature TCAT are equal to or lower than a predetermined temperature.
[0041]
FIG. 7 is a timing chart of a control operation example according to the present embodiment. When the ignition switch is turned on at time t0 (FIG. 7A), the ECU 5 changes the regulator control voltage VC to a predetermined voltage VC1 for normal operation. And the power generation mode 1 is set ((f) and (h) in the same figure). When the starter is turned on at time t1 after a lapse of time TD (for example, the time required for turning the key (about 0.1 second)) from time t0, the rotation of the engine is started ((b) and (c) in FIG. 4). As the engine speed NE increases, the alternator output voltage VALT increases to the battery charging voltage VCHG ((g) in the figure).
[0042]
When the engine speed NE reaches the predetermined number of revolutions NEK for complete explosion determination (time t2), the ECU 5 determines that the explosion is complete ((c) and (d) in FIG. 5), and switches the switch 23 from the terminal 23b to the 23c. A switching control signal is output (FIG. 4E). At this time, considering the time required for switching the switch 23 (the time from the output of the control signal to the actual completion of the switching, for example, about 0.25 seconds) ΔT, the regulator control is performed at time t3 after ΔT has elapsed from time t2. The voltage VC is set to the EHC control voltage VC2 such that the alternator output voltage VALT becomes the VEHC value corrected in step S5 in FIG. 3, and the mode shifts to the power generation mode 2 (FIGS. (F) and (h)). As a result, the alternator output voltage VALT rises to the VEHC value ((g) in the figure), and the temperature of the EHC 16 starts to rise ((i) in the figure). Here, the EHC control voltage VC2 is feedback-controlled so that the detected supply voltage (the voltage of the connection line 30 in FIG. 2) matches the determined VEHC value.
[0043]
Then, at time t4 after the time TON determined in step S3 of FIG. 3, the regulator control voltage VC is returned to the VC1 value and the operation returns to the power generation mode 1 (FIGS. (F) and (h)). As a result, the alternator output voltage VALT becomes the normal battery charging voltage VCHG ((g) in the figure). The ECU 5 outputs a control signal for switching the switch 23 from the terminal 23c side to the 23b side at a time t5 after a lapse of time ΔT from the time t4, and ends the control at the time of starting the engine ((e) in the figure).
[0044]
In this embodiment, the air pump motor 27 is operated at the same timing as when the EHC 16 is turned on.
[0045]
The determination time TCHK, which is a parameter indicating the degree of deterioration of the catalyst, is calculated during feedback control for calculating the air-fuel ratio correction coefficient KO2 based only on the output RVO2 of the downstream O2 sensor 16, as shown in FIG. O2 sensor after the generation of the special P-term PRSP for skipping the TL and KO2 values in the increasing direction from the occurrence of the special P-term PLSP for skipping in the decreasing direction to the inversion of the O2 sensor output RVO2 The time TR until the output RVO2 is inverted is measured, and the measurement is performed based on these times TL and TR.
[0046]
FIG. 8 is a flowchart of a program for performing this calculation. In step S21 in FIG. 8, it is determined whether or not a precondition for calculating the degree of deterioration is satisfied. This precondition is satisfied when engine operating parameters such as the engine speed NE and the intake pipe absolute pressure PBA are within a predetermined range, and the engine operating state is in a steady state.
[0047]
When the precondition is not satisfied, the process proceeds to step S22, in which the integrated values TLSUM and TRSUM of the times TL and TR and the number of times nTL and nTR of measuring the TL value and the TR value are reset to 0, and normal fuel control is performed (step S23). . In the normal fuel control, the correction coefficient KO2 is calculated by feedback control based on the outputs of the O2 sensors 16 and 17 during the air-fuel ratio feedback control, while it is set to a predetermined value according to the engine operating state during the open loop control.
[0048]
When the precondition is satisfied, the process proceeds to step S24, in which it is determined whether the measurement of the TL value and the TR value has been performed a predetermined number of times. Since the answer is initially negative (NO), the process proceeds to step S25, and the downstream O2 In addition to performing PI (proportional integration) control based only on the sensor output RVO2, the TL value and the TR value are measured, and integrated values TLSUM and TRSUM of those values are calculated (steps S25 and S26).
[0049]
Specifically, as shown in FIG. 9, at a time t2 when a predetermined time tLD has elapsed from the lean-rich inversion time t1 of the downstream O2 sensor output RVO2, the KO2 value is skipped in the decreasing direction by the special P-term PLSP in the lean direction. Then, I-term control is performed to gradually reduce the KO2 value from the rich lean inversion point t3 of the sensor output RVO2 to a time point t4 at which a predetermined time tRD elapses. At this time, the time from time t2 to time t3 is measured as a TL value (TL1). Next, at time t4, the KO2 value is skipped in the increasing direction by the special P-term PRSP in the rich direction, and thereafter, the KO2 value is gradually increased from the lean-rich inversion time t5 of the sensor output RVO2 to a time t6 at which a predetermined time tLD has elapsed. I do. Then, the time from time t4 to time t5 is measured as a TR value (TR1). Thereafter, TL2, TR2,... Are sequentially measured in the same manner, and TLSUM and TRSUM are calculated as integrated values of the measured values.
[0050]
When the answer to step S24 is affirmative (YES), that is, when the measurement of the predetermined number of times is completed, the determination time TCHK is calculated by the following equation (step S27).
[0051]
TCHK = (TLSUM / nTL + TRSUM / nTR) / 2
Thereafter, normal fuel control is performed in the same manner as in step S23 (step S28).
[0052]
Here, TCHK, which is the average value of the times TL and TR, has a relationship as shown in FIG. 10 with the purification rate of the catalyst (CAT purification rate), and as the purification rate of the catalyst decreases, the TCHK value decreases. I do. Therefore, in FIG. 10, in the range where the TCHK value decreases as the purification rate decreases, the TCHK value indicates the degree of deterioration of the catalyst (the degree of reduction of the purification rate). Note that the purification rate of the catalyst depends on the oxygen storage capacity of the catalyst, and a decrease in the determination time TCHK means a decrease in the O2 storage capacity. By this method, the degree of deterioration of the catalyst can be accurately grasped.
[0053]
In the above-described embodiment, the voltage supplied to the EHC 16 and the energizing time are both set according to the engine coolant temperature TW and the intake air temperature TA, but the energizing time may be constant. Further, the voltage VECH and the energization time TON may be set using the catalyst temperature TCAT detected by the catalyst temperature sensor 19 instead of either the engine water temperature TW or the intake air temperature TA. Alternatively, the voltage VECH and the energization time TON may be set according to one or two of the engine water temperature TW, the intake air temperature TA, and the catalyst temperature TCAT. Further, instead of the catalyst temperature TCAT, a parameter representing the temperature of the exhaust system such as the exhaust gas temperature may be used.
[0054]
【The invention's effect】
As described in detail above, according to the present invention, electric power is supplied from the alternator to the electrically heated catalyst, and the generated voltage of the alternator is controlled according to the detected time-dependent change state of the electrically heated catalyst. It is possible to accurately control the temperature of the catalyst in accordance with the change with time of the catalyst, and to prevent an excessive rise in temperature in a new state and deterioration of exhaust gas characteristics at the time of characteristic deterioration.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an internal combustion engine and a control device thereof according to an embodiment of the present invention.
FIG. 2 is a circuit diagram showing a connection state of a heater resistance and the like of an electrically heated catalyst.
FIG. 3 is a flowchart of a process for controlling a voltage supplied to an electrically heated catalyst and an energizing time.
FIG. 4 is a diagram showing a table used in the processing of FIG. 3;
FIG. 5 is a diagram showing a table and the like used in the processing of FIG. 3;
FIG. 6 is a diagram showing a table used in the processing of FIG. 3;
FIG. 7 is a timing chart of a control operation example in the present embodiment.
FIG. 8 is a flowchart of a process for calculating a parameter indicating a degree of deterioration of a catalyst.
FIG. 9 is a diagram for explaining a method of calculating a parameter indicating a degree of deterioration of a catalyst.
FIG. 10 is a diagram showing a relationship between a purification rate by a catalyst and a parameter representing a degree of deterioration.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Internal combustion engine 5 Electronic control unit 9 Intake temperature sensor 10 Engine water temperature sensor 16 Electric heating type catalyst 18 Three-way catalyst 20F, 20R Oxygen concentration sensor 21 Alternator 22 Regulator 23 Changeover switch

Claims (3)

An alternator driven by an internal combustion engine to generate electric power,
Regulator means for controlling the voltage generated by the alternator;
An electrically heated catalyst provided in an exhaust system of the engine and electrically heated by electric power generated by the alternator;
Time-varying state detecting means for detecting a time-varying state of the electrically heated catalyst ,
The generated voltage determined in accordance with the output of該経during changing state detecting means, further comprising a regulator control means for controlling the regulator means in order to be supplied to the electrically heated catalyst of the power generation voltage that is the determined from the alternator An exhaust gas purifying apparatus for an internal combustion engine. Comprising operating condition detecting means for detecting operating conditions of said engine, said regulator control means is an exhaust of an internal combustion engine according to claim 1, wherein the determining the power voltage in accordance with the engine operating state of the detected Gas purification device. The regulator control means further determines a time when the power generation voltage is to be supplied to the electrically heated catalyst in accordance with the detected engine operating state , and, over the determined time, the determined power generation voltage The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, wherein the regulator means is controlled so that the pressure is supplied from the alternator to the electrically heated catalyst .

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